A lithographic apparatus includes a displacement measuring system to measure a position of a moveable object with respect to a reference frame of the lithographic apparatus, in at least three coplanar degrees of freedom (x, y, Rz) of an orthogonal x-y-z coordinate system centered in the center of the moveable object. The moveable object includes a support structure configured to support a patterning device or a substrate table configured to support a substrate. The displacement measuring system includes at least three sensor heads, each sensor head being positioned with a measuring direction substantially coplanar with the x-y plane of the coordinate system and each sensor head being furthermore positioned with the measuring direction substantially perpendicular to a connection line connecting the sensor head with the center of the movable object and extending coplanar with the x-y plane.